How to index pages on the site?

Question

Search Engine Optimization

Hello! I'm building a classifieds website.
There are 15 ads displayed per page.
Let's say that today there are 35 ads = 3 pages on the site in the "home" section.
And tomorrow 10 products are sold and only 2 pages remain.
How to be with the third from the point of view of search engine optimization? After all, it is indexed and the 404 response will not work, but the user also needs to transfer something on the 3rd page (they say no ads were found)

Answer 1

ты и не должен удалять объявления. все ссылки должны оставаться на своих местах. просто при переходе на уже проданную страницу - объявление должно быть закрытым. ("Извините, это объявление не актуально" и т.д.) и закрыть кнопки связи с продавцом и т.д. чтобы человек просто видел название обьявления и текст который раньше был. и все.

Answer 2

Oddly enough, the most correct thing from the point of view of search engines would be to show the page, then give a 404 error if it does not exist. In total, she would either appear in the search or disappear from it.
As I understand it, this does not suit you, the second option (you mentioned it in the question): always keep this page, but program it so that if there are no ads on it, then place some kind of stub there. Another thing is if there are many such pages, then the stubs must be made different. search engines do not like duplicates, besides, it must be textual. But this is a rather complex logic and complex troubles.
The third option is to see, think about how many visitors such pages bring throughout the site, it happens that they go exclusively to internal sections and it’s easier to close such section pages from indexing in robots.txt and then the problem will disappear by itself.